Implantable leads are a critical component in medical device applications. In any implantable medical device (IMD) application, and particularly in pacemaker or implantable cardiac defibrillator applications, it is important to be able to monitor and report the performance and functional status of leads. In some IMD applications, the lead status is monitored for malfunctions, for example, when the lead fractures and is unable to perform.
In one example, the impedance of a lead conductor coupled with an electrode is measured to monitor the status of a lead as described in U.S. Pat. No. 4,958,632. Exposure of the lead to the surrounding environment of the body or fracture of the lead causes measurable changes in the conductor impedance, which signals that the lead has malfunctioned or is beginning to fail. However, conventional lead status monitoring techniques are not able to detect breaches of the lead insulation until the lead conductor impedance changes, which occurs only when the lead has begun to malfunction. In other words, the techniques are only able to detect failure of the lead as the lead conductor begins to fail.
U.S. Pat. No. 6,317,633, is another example of lead conductor monitoring through impedance measurements. However, the system does not address the issue that the lead conductor impedance only changes upon onset of failure in the lead conductor, and not before, when only the insulation has been partially breached and the lead is still fully functional.
What is needed are implantable leads that overcome the shortcomings of previous implantable leads. What is further needed are implantable leads that permit functional status monitoring of lead insulation before the onset of lead conductor failure, which would allow replacement of a lead before degradation in performance.